1. Field of the Invention
The present invention relates to an imaging lens for solid-state imaging elements for use in small imaging devices for use in small, thin electronic apparatuses such as mobile terminals and PDAs (personal digital assistances).
2. Description of the Related Art
As the market for mobile terminals including an imaging device expands in recent years, a small, high-pixel-number, solid-state imaging element has been mounted on such imaging devices.
With such miniaturization and pixel number increase of imaging elements, imaging lenses have been required to achieve higher performance in resolution and image quality. Further, with their widespread use, imaging lenses have been required to be more low-cost.
To meet such high performance trend, imaging lenses including multiple lenses have been commonly used. In recent years, there have been proposed four-lens-structure imaging lenses that can achieve higher performance than two to three-lens-structure ones.
As such a four-lens-structure imaging lens, for example, Japanese Patent Laid-Open Publication No. 2008-33376 (Patent Document 1) discloses a high-performance-oriented imaging lens where an aperture stop, a first lens having positive refractive power, a second lens having negative refractive power, a third lens having positive refractive power, and a fourth lens having at least one aspherical surface are arranged in this order from the object side.
Japanese Patent Laid-Open Publication No. 2009-14899 (Patent Document 2) discloses an imaging lens that is intended to increase the performance by arranging an aperture stop, a biconvex first lens having positive refractive power, a meniscus-shaped second lens directing a convex surface toward an object and having negative refractive power, a meniscus-shaped third lens directing a convex surface toward an image and having positive refractive power, and a meniscus-shaped fourth lens directing a convex surface toward the object and having negative refractive power in this order from the object side of the imaging lens.
While the imaging lenses described in Patent Documents 1 and 2 are intended to increase the performance by employing a four-lens structure, they are insufficient to meet miniaturization and slimming down or correct aberrations.